Tire crown reinforcement with specified rubber decoupling layers

ABSTRACT

A tire having a crown, two sidewalls and two beads, a carcass reinforcement anchored in the two tire beads and a belt reinforcement, the belt reinforcement including at least two superposed reinforcing plies formed by cords parallel in each ply and criss-crossed from one to the other forming with the circumferential direction angles (α, β) ranging between 10° and 70° and characterized in that, there is provided, between the two superposed reinforcing plies, at least two axially adjacent rubber decoupling layers with different mechanical properties and in that each of the two rubber decoupling layers is in contact with the cords of the two superposed reinforcing layers.

BACKGROUND OF THE INVENTION

This is a divisional application of U.S. Ser. No. 09/823,542 filed onMar. 30, 2001 and which is a continuation of International applicationPCT/EP99/07263 filed Oct. 1, 1999, which claims priority under 35 U.S.C.§§ 119 and/or 365 to patent application Serial No. 98/12594 filed inFrance on Oct. 3, 1998, the entire content of which is herebyincorporated by reference.

The invention concerns the crowns of tires and, notably, the rubberdecouplings placed between the reinforcing plies of those crowns.

The crowns of tires usually comprise a carcass reinforcement, a beltreinforcement with usually at least two superposed reinforcing pliesformed by cords parallel in each ply and criss-crossed from one ply tothe other and a tread.

The crowns of tires are in contact with the road and must transmit tothe wheel, by means of the sidewalls and beads, the transverse stressesnecessary to steer the vehicles. For the road performance of vehicles tobe satisfactory, it is necessary for the crowns to be very rigidrelative, for example, to the sidewalls. A permanent objective is to tryto obtain such high rigidity as simply and economically as possible.

It is well known that the rubber decouplings of belt reinforcing cordscontribute to obtaining high rigidity. That is why those rubberdecouplings usually have a high modulus of elasticity. On the otherhand, the rubber decouplings in contact with the cords of carcassreinforcements usually have a low modulus of elasticity because theymust withstand without damage the high deformations they undergo in thesidewalls of the tires.

On the other hand, a great deal of research is being conducted to reducethe gasoline consumption of road vehicles. For that purpose, emphasis ison the design of tires having a very low rolling resistance, whilemaintaining the other properties of wear, adherence, performance, etc.,as economically as possible.

SUMMARY OF THE INVENTION

The object of the invention is a tire whose crown structure is improvedin order to facilitate its manufacturing process and thus make it moreeconomical, as well as to improve its quality and its performances.

The object of the invention, according to a first variant, is also anembodiment intended mainly to lower the resistance to rolling and,according to a second variant, an embodiment intended to improve therigidity of the crown.

In what follows, “cord” is understood to mean monofilaments as well asmultifilaments, or assemblages like cables, yarns or even any type ofequivalent assemblage, whatever the material and treatment of thosecords, such as surface treatment or coating, notably, of rubber havingundergone the start of vulcanization or pre-sizing to promote adhesionon the rubber.

The “rubber decoupling layer” between two reinforcing plies isunderstood to mean a rubbery compound in contact with the reinforcingplies of at least one of the two plies, adhering to the latter andfilling the interstices between adjacent cords. In current industrialpractice, the reinforcing plies are made by application of calenderedplies; consequently, between two given reinforcing plies, two rubberdecoupling layers are used, each being in contact with the cords of oneof the two plies and having the same composition for the different zonesof the tire.

“Contact” between a cord and a rubber decoupling layer is understood tomean that at least one part of the outer circumference of the cord is inclose contact with the rubbery compound constituting the rubberdecoupling. If the cord contains a covering or coating, the term contactmeans that the outer circumference of that covering or coating is inclose contact with the rubbery compound constituting the rubber bonding.

“Modulus of elasticity” of a rubbery compound is understood to mean asecant extension modulus obtained on a uniaxial extension deformation inthe order of 10% after three cycles of accommodation and at ambienttemperature.

Upon a sinusoidal stress of a rubbery compound, for example, withdeformation applied, ε*=ε₀e^(j(w+t)), the steady state response of thatcompound is also sinusoidal and dephased by an angle δ,σ₀e^(j(wt+δ)). Acomplex modulus G*=σ*/ε*=σ₀/ε₀e^(jσ)=G′+jG″ is defined, with a thestress in MPa. G′ is called “dynamic modulus” and G″ is called dynamicmodulus of loss. The tan δ=G″/G′ ratio is called damping ratio. Themeasurements are made on alternate shear stress at a frequency of 10 Hz,at a temperature of 60° C. and at a peak-to-peak dynamic deformation of10%.

The tire according to the invention comprises a crown, two sidewalls andtwo beads, a carcass reinforcement anchored in the two beads and a beltreinforcement, that belt reinforcement comprising at least twosuperposed reinforcing plies formed by cords parallel in each ply andcriss-crossed from one ply to the other by forming angles (α, β) withthe circumferential direction ranging between 10° and 70°. That tire ischaracterized in that, between the two superposed reinforcing plies, atleast two rubber decoupling layers of different mechanical propertiesare placed axially adjacent, and in that each of said two rubberdecoupling layers is in contact with the cords of said two superposedreinforcing plies.

That tire has the advantage of having only one single rubber decouplinglayer between the two crown reinforcing plies in any circumferentialsection (outside of the zones of transition between the two adjacentrubber decoupling layers). This layer can have different properties indifferent circumferential sections, for example, in the center and onthe edges of the plies. That makes it possible to adapt the nature andthe properties of the single layer to the objective of the tiredesigner.

The rubber decoupling layers are preferably made by a spiral winding ofa rubbery compound section directly on the cords of the radially innerreinforcing ply. That direct application of rubber decoupling layers onthe cords of the reinforcing plies simplifies manufacture of the tire.

A first decoupling layer is placed between the center part of the twosuperposed reinforcing plies and a second decoupling layer is placed onat least one side of the first layer and extends at least as far as thecorresponding lateral ends of the two superposed reinforcing plies. In aparticular embodiment, a second decoupling layer extends axially morethan 3 mm beyond a lateral end of the cords of a reinforcing ply.

In a first embodiment, the ratio between the moduli of elasticity of thesecond layer and first layer ranges between 0.05 and 0.8 and preferablybetween 0.4 and 0.6.

In that embodiment, the modulus of elasticity of the rubber decouplingsbetween the two reinforcing plies consisting of crossed cords ismarkedly less in at least one lateral zone of the tire crown than thatof the rubber decouplings in the center zone of the crown. This has theadvantage of making substantial gains in running resistance possible bymaintaining the drift thrust and rolling lifetime properties at totallyacceptable levels.

The second rubber decoupling layer preferably has a damping ratio tan δbelow 0.08. Such a layer is very easily hysteretic and markedlycontributes to the gain in running resistance of the tire concerned.

It is also possible, in order to preserve or improve the drift thrustand lifetime properties, to add, on the same side as the; second rubberdecoupling layer, an additional reinforcing ply consisting of cordsoriented in the circumferential direction and extending axially roughlylike the second rubber decoupling layer, for example havingsubstantially the same inner and outer axial extension as the secondrubber decoupling layer. That additional reinforcing ply can be placedradially outside or inside the two superposed reinforcing plies orbetween those two plies.

This first embodiment of a tire is suited, in particular, to tires ofH/W aspect ratio higher than 0.55

According to a second embodiment, the ratio between the moduli ofelasticity of the second rubber decoupling layer and first layer rangesbetween 1.2 and 20 and preferably between 1.5 and 10.

In that second embodiment, it is the first rubber decoupling layer,arranged in the center zone of the two reinforcing plies, which has alow modulus of elasticity, less than that of the rubber decoupling layerarranged in the lateral zone of the tire crown.

That second embodiment also has the advantage of making it possible toreduce the running resistance without impairing the drift thrust andlifetime properties. That second embodiment is of particular value withtires of aspect ratio below 0.55.

According to another embodiment of the invention, the two reinforcingplies between which two rubber decoupling layers of different mechanicalproperties are axially placed are a crown reinforcing ply and a carcassreinforcing ply. That embodiment is particularly advantageous when thebelt reinforcement consists of a reinforcing ply whose cords areoriented relative to the circumferential direction at an angle α,ranging between 10° and 70° and of a reinforcing ply formed by parallelcords oriented roughly circumferentially.

DESCRIPTION OF THE DRAWINGS

FIG. 1 presents in partial meridian section a tire crown according tothe invention;

FIG. 2 presents in partial meridian section a working variant of thetire crown of FIG. 1;

FIG. 3 presents in partial meridian section a working variant of thetire crown of FIG. 2;

FIG. 4 presents in partial meridian section a second working variant ofthe tire crown of FIG. 2;

FIG. 5 presents in partial meridian section a second working variant ofa tire crown;

FIG. 6 presents in partial meridian section a working variant of thetire crown of FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, a first embodiment of a tire crown according to the inventionis presented schematically in partial meridian section. That crown 1comprises a tread 2 and two crown reinforcing plies 3 and 4. The twoplies are called crossed plies, they are superposed and they consist ofcords parallel in each ply and criss-crossed from one ply to the otherby forming angles (α, β) with the circumferential direction rangingbetween 10 and 70°. Between the two plies 3 and 4 there are two rubberdecoupling layers, layer 6 in the center part of the plies and layer 10in the lateral part of the plies. The two rubber decoupling layers 6 and10 are both in contact with the cords of the two plies 3 and 4. Theboundary of separation between the two layers 6 and 10 is preferablybeveled.

Radially below ply 4, in the zone referenced 8, the crown 1 contains aradial carcass reinforcement not represented.

The cords of plies 3 and 4 are arranged so that they have no contactwith each other.

The first rubber decoupling layer 6 usually has a modulus of elasticityranging between 10 and 15 MPa.

In the lateral part of the crown, the cords of the two plies 3 and 4 arein contact with a second rubber decoupling layer 10 of modulus ofelasticity less than that of the first layer. The ratio of moduli rangesbetween 0.05 and 0.8 and preferably between 0.4 and 0.6 and morepreferably between 0.5 and 0.7. That layer of lower modulus limits theamplitude of the maximum shear stresses at the ends of the plies andtherefore limits the energies dissipated by hysteresis on rolling.

FIG. 2 presents a working variant of the tire crown of FIG. 1, in whicha partial ply 11 has been added. That ply 11 consists of cords orientedin the circumferential direction of the tire. Those cords can be oftextile material, aramide, polyester, nylon, glass fiber or wire.

Ply 11 is placed outside the two plies 3 and 4 and axially extends justroughly above the two lateral ends of plies 3 and 4, for example havingsubstantially the same outer axial extension as the axially widest ply4. That ply has the advantage of limiting the amplitude of the shearstresses between the ends of both plies 3 and 4 and thus preserving andeven increasing the drift thrust and lifetime (in the sense ofendurance) properties, while having substantially improved the runningresistance of the tire.

That ply 11 can also be placed radially inside the two plies 3 and 4(FIG. 3) as well as radially between the two plies 3 and 4 (FIG. 4).

This embodiment with a rubber decoupling layer of lesser modulus and lowhysteresis between the two crossed reinforcing plies and at least one ofthe lateral ends of the crown is particularly suited to tires of H/W(height divided by width) aspect ratio higher than 0.55.

According to another embodiment of the invention, a substantial gain indrift thrust of the tires can also be obtained by inverting the ratio ofmoduli of elasticity between the first and second layers. The layer ofhigher modulus of elasticity is thus placed at the lateral ends of thecrown and that of lower modulus and lower hysteresis is placed in thecenter part between the two crossed reinforcing plies 3 and 4.

The rubber decoupling layers arranged toward the lateral ends of thecrown have a length of contact with the cords of the crossed reinforcingply of least axial width, ply 3, which must be axially greater than 5 mmand preferably greater than 20 mm in order to be effective. But it isnot necessary to increase that contact length beyond ⅓ of the axialwidth of ply 3.

This second embodiment is particularly well suited to tires of aspectratio below 0.55.

The 175/70—13 tires were made with the following configurations:

-   -   Control A contained a wire crown (in 6.23 NF cords at 80 f/dm        oriented at 23°) with a single rubber decoupling layer between        both plies 3 and 4 of modulus of elasticity 12 MPa;    -   Tire B with two rubber decoupling layers between the two crossed        reinforcing plies, layer 6 of modulus of elasticity 12 MPa and        layer 10 of modulus of elasticity 5 MPa;    -   Tire C, second control, similar to tire A, but with a single        rubber decoupling layer between both plies 3 and 4, of modulus        of elasticity 5 MPa;    -   Tire D, similar to tire B, but with, in addition, a ply 11 of        Nylon 140*2 cords oriented circumferentially above the lateral        ends of the two crossed reinforcing plies.

The tires underwent a rolling resistance (at 60 km/h, pressure 2.1 barsand load 3500 N). That test measures the energy dissipated on rollingand a favorable result is expressed by a figure below 100. They alsounderwent a characterization of their drift thrust, that is, of thelateral stress Y developed by the tire on rolling at an applied driftangle δ. An increase of drift thrust is expressed by a figure higherthan 100. The test was performed with a load of 3500 N and an inflationpressure of 2 bars.

TIRE RR Y(δ) A 100 100 B 95 95 C 94 80 D 95 105

Solution B, according to the invention, showed a marked improvement inrolling resistance with a limited reduction of drift thrust.

Solution C presents the same improvement in rolling resistance, but witha much sharper reduction of drift thrust.

Finally, solution D, according to the invention, presents an improvementof tire properties in both tests undergone.

Those tests show the importance of being able to adjust the rigidity andhysteresis of the rubber decoupling layers between the two crossed crownreinforcing plies to the circumferential section of the tire accordingto the objective of the tire designer.

FIG. 5 presents another embodiment of the invention. The crown 20 ofthat tire comprises a tread 22, a crown reinforcing ply 23 whose cordsform angles α with the circumferential direction ranging between 10 and70 degrees and a carcass reinforcing ply 24. Between the two superposedreinforcing plies there is a first rubber decoupling layer 25 and anadjacent second rubber decoupling layer 26. Those layers are directly incontact with the cords of the two reinforcing plies 23 and 24. Layer 25is placed in the center of the two plies and layer 26 is placed in alateral zone. Such a tire also has an additional ply in its crownreinforcement, containing circumferentially oriented wire or other cords(not represented in FIG. 5).

The modulus of elasticity and/or the damping ratio tan δ of the twolayers 25 and 26 can vary like the two working variants previouslydescribed.

In FIG. 6, a working variant 30 of the tire crown of FIG. 5 ispresented. In that figure, the additional crown reinforcing ply 31containing circumferentially oriented wire or other cords isrepresented. The crown 30 further contains a partial ply 32 placedradially inside both the carcass ply 24 and crown reinforcing ply 23.That ply 32 appreciably improves the drift thrust, running resistanceand lifetime properties of the tire when the rubber decoupling layer oflesser modulus and low hysteresis is placed at the lateral ends of thecrown.

In the other embodiment consisting of placing the rubber decouplinglayer of highest modulus laterally, the partial ply 32 furtherreinforces the gain in drift thrust of the tire. That applies to tiresintended to roll at very high speed.

In manufacturing the different tires according to the invention, it isvery advantageous to fabricate them on a rigid core setting the shape ofthe inner cavity. All the constituents of the tire are applied on thatcore, in the order required by the final architecture, being directlyarranged in their final place, without undergoing shaping at any time offabrication. That fabrication can, notably, use the devices described inpatent EP 0,243,851 laying the cords of the carcass reinforcement, EP0,248,301 for laying the crown reinforcements and EP 0,264,600 forlaying the rubbery compounds. The rubber decoupling layers are thuspreferably made by spiral winding of a rubbery compound section directlyon the cords of the radially inner reinforcing ply. The tire can bemolded and vulcanized, as explained in U.S. Pat. No. 4,895,692.

1. A tire comprising a crown, two sidewalls and two beads, a carcassreinforcement anchored in the two beads and a belt reinforcement, saidcarcass reinforcement comprising at least one reinforcing ply made up ofparallel cords forming an angles roughly equal to 90° with thecircumferential direction and said belt reinforcement comprising atleast one reinforcing ply made up of parallel cords forming angles αwith the circumferential direction ranging between 10° and 70°,characterized in that, between said crown reinforcing ply and saidcarcass reinforcing ply, at least two rubber decoupling layers ofdifferent mechanical properties are placed axially adjacent, and in thateach of said two rubber decoupling layers is in contact with the cordsof said two superposed reinforcing plies.
 2. A tire according to claim1, in which the belt reinforcement consists of a reinforcing ply made upof parallel wires forming an angle α with the circumferential directionranging between 10° and 70° and of a reinforcing ply made up of parallelcords oriented roughly circumferentially.
 3. A tire according to claim 1in which each rubber decoupling layer is made by a spiral winding of arubbery compound section directly on the cords of the radially innerreinforcing ply.
 4. A tire according to claim 1, in which a firstdecoupling layer is placed between the center part of the said twosuperposed reinforcing plies, and in which a second decoupling layer isplaced on at least one side of the first layer and extends at least asfar as the corresponding lateral ends of the said two superposedreinforcing plies.